An "X bore" is someone who seems to be obsessed with some aspect of X. "He is a football bore." = "He only talks about football and this becomes boring as a subject of conversation."
A 'sock bore' would be someone who appears to be obsessed with some aspect of their socks - what they are like, where they are kept, how they are washed, etc. In the context (little though it is) I think he means that his wife is fed up with his talking about his socks.
These sentences are from a column called 'the Odd Couple by Richard Brooks from The Observer that was reprinted in Reading 4 Student's Book: Advanced Simon Greenall, Diana Pye (1993)
It is a humorous article on what the author calls the "Missing Sock Syndrome" [=MSS] and his efforts to find out why socks disappear and sometimes reappear. The paragraphs preceding the sentences under discussion this give examples of other people's lack of concern about missing socks. This is the final paragraph:
Only my nine-year-old daughter shows some early signs of inheriting her father's MSS concerns. My wife thinks I'm a sock bore. But then I noticed that my socks regularly turn up on my wife's feet --- she is cavalier when it comes to hosiery.
I am posting this to demonstrate that without complete context and source, people can only make plausible guesses as to what a 'sock bore' might mean. We need the actual context to know that the people who said that he was a 'sock bore' because he talked too much about socks were correct.